1. Field of the Invention
The present invention relates to printers which use ultrasonic energy to transfer dye from a dye carrier to a receiver.
2. Description of the Prior Art
Some thermal printer apparatus use a dye transfer process. In this process, a carrier containing a dye is disposed between a receiver, such as paper, and a print head formed of for example a plurality of individual thermal heat producing elements often referred to as heating elements. The receiver and carrier are generally moved relative to the print head which is fixed. When a particular heating element is energized, it is heated and causes dye to transfer (e.g. by diffusion) from the carrier to an image pixel in the receiver. The density, or darkness, of the printed dye is a function of the temperature of the heating element and the time the carrier is heated. In other words, the heat delivered from the heating element to the carrier causes dye to transfer to an image pixel of a receiver. The amount of dye is directly related to the amount of heat transferred to the carrier.
Thermal dye transfer printer apparatus offer the advantage of true "continuous tone" dye density transfer. By varying the heat applied by each heating element to the carrier, a variable dye density image pixel is formed in the receiver. A problem with this type of arrangement is that the printing rate is limited due to the "cool down" time for each heating element. A second problem is that the area of the heating element generally produces large image pixels which is a limiting factor in providing high image resolution. A third problem is that substantial power is required to produce images, because not only the dye is heated, but also the support and heating element itself. A still further problem is caused by the fact that the dye carrier must be made rather thin to reduce the amount of heat needed and to provide image sharpness. Thin webs are hard to handle and difficult to manufacture.
In the proceedings of 7th Symposium on Ultrasonic Electronics, Kyoto 1986 Japanese Journal of Applied Physics, Vol. 26 (1987) Supplement 26-1, pp. 141-143, Sakurai et al discuss an ultrasonic piezoelectric apparatus where a printing wire is mechanically vibrated at 146 KH to heat and transfer a thermoplastic ink. The resolution of this system is limited to the mechanical dimensions of the printing wire.